Showing papers in "Sensors and Actuators B-chemical in 2022"

A high-performance room temperature benzene gas sensor based on CoTiO3 covered TiO2 nanospheres decorated with Pd nanoparticles

Abstract: A benzene sensor based on Pd doped CoTiO3/TiO2 (Pd-CTT) nanocomposite was reported in this paper. The surface morphology and structure composition of the samples were investigated by SEM, TEM, XRD and XPS. The benzene sensing performance of the sensors with different ratios of CoTiO3 and TiO2 was studied at room temperature (RT) of 25 °C. The gas sensing performance of the sensor was further improved by the construction of Pd-CTT ternary composite sensing material. The results show that the sensor has remarkable sensing performance for benzene, including excellent linear response, rapid detection speed, good repeatability and stability. The Pd-CTT sensor showed a high response (Rg/Ra = 33.46 @ 50 ppm) to benzene, with detection limit as low as 100 ppb. The excellent benzene sensing properties of Pd-CTT sensor are attributed to the formation of CoTiO3/TiO2 p-n heterojunction and catalytic action of Pd. This work highlights the unique advantage of Pd-CTT nanocomposite for benzene sensor.

A high-performance room temperature benzene gas sensor based on CoTiO3 covered TiO2 nanospheres decorated with Pd nanoparticles

Abstract: A benzene sensor based on Pd doped CoTiO3/TiO2 (Pd-CTT) nanocomposite was reported in this paper. The surface morphology and structure composition of the samples were investigated by SEM, TEM, XRD and XPS. The benzene sensing performance of the sensors with different ratios of CoTiO3 and TiO2 was studied at room temperature (RT) of 25 °C. The gas sensing performance of the sensor was further improved by the construction of Pd-CTT ternary composite sensing material. The results show that the sensor has remarkable sensing performance for benzene, including excellent linear response, rapid detection speed, good repeatability and stability. The Pd-CTT sensor showed a high response (Rg/Ra = 33.46 @ 50 ppm) to benzene, with detection limit as low as 100 ppb. The excellent benzene sensing properties of Pd-CTT sensor are attributed to the formation of CoTiO3/TiO2 p-n heterojunction and catalytic action of Pd. This work highlights the unique advantage of Pd-CTT nanocomposite for benzene sensor.

Molecularly imprinted polymer based electrochemical sensor for quantitative detection of SARS-CoV-2 spike protein

Abstract: The continued spread of the coronavirus disease and prevalence of the global pandemic is exacerbated by the increase in the number of asymptomatic individuals who unknowingly spread the SARS-CoV-2 virus. Although remarkable progress is being achieved at curtailing further rampage of the disease, there is still the demand for simple and rapid diagnostic tools for early detection of the COVID-19 infection and the following isolation. We report the fabrication of an electrochemical sensor based on a molecularly imprinted polymer synthetic receptor for the quantitative detection of SARS-CoV-2 spike protein subunit S1 (ncovS1), by harnessing the covalent interaction between 1,2-diols of the highly glycosylated protein and the boronic acid group of 3-aminophenylboronic acid (APBA). The sensor displays a satisfactory performance with a reaction time of 15 min and is capable of detecting ncovS1 both in phosphate buffered saline and patient’s nasopharyngeal samples with LOD values of 15 fM and 64 fM, respectively. Moreover, the sensor is compatible with portable potentiostats thus allowing on-site measurements thereby holding a great potential as a point-of-care testing platform for rapid and early diagnosis of COVID-19 patients.

Detection of four alcohol homologue gases by ZnO gas sensor in dynamic interval temperature modulation mode

Abstract: Metal oxide semiconductor (MOS) gas sensors have poor selectivity, especially in volatile organic compounds (VOCs). Dynamic measurement method of gas sensors can bring a potential to resolve this problem. However, it is also a challenge to distinguish homologue gases with the same functional group. In this paper, four alcohol homologue gases were detected by a ZnO gas sensor. The period of triangular wave is changed to explore the optimal temperature range in dynamic interval temperature modulation mode for detecting ethyl alcohol, n-propyl alcohol, isopropyl alcohol and n-butyl alcohol. The experimental results show that only when the low temperature is lower than 180 °C and the high temperature is higher than 460 °C, the unsaturation phenomenon can be solved, so as to realize the qualitative and quantitative analysis of the four alcohol homologue gases. Under this experimental condition, the concentration gradient measurement of 100–400 ppm is carried out. After the optimization with the decision tree classification algorithm, the recognition accuracy of the four alcohol homologue gases is 97.62%.

Detection of four alcohol homologue gases by ZnO gas sensor in dynamic interval temperature modulation mode

Abstract: Metal oxide semiconductor (MOS) gas sensors have poor selectivity, especially in volatile organic compounds (VOCs). Dynamic measurement method of gas sensors can bring a potential to resolve this problem. However, it is also a challenge to distinguish homologue gases with the same functional group. In this paper, four alcohol homologue gases were detected by a ZnO gas sensor. The period of triangular wave is changed to explore the optimal temperature range in dynamic interval temperature modulation mode for detecting ethyl alcohol, n-propyl alcohol, isopropyl alcohol and n-butyl alcohol. The experimental results show that only when the low temperature is lower than 180 °C and the high temperature is higher than 460 °C, the unsaturation phenomenon can be solved, so as to realize the qualitative and quantitative analysis of the four alcohol homologue gases. Under this experimental condition, the concentration gradient measurement of 100–400 ppm is carried out. After the optimization with the decision tree classification algorithm, the recognition accuracy of the four alcohol homologue gases is 97.62%.

Influence of Major Parameters on the Sensing Mechanism of Semiconductor Metal Oxide based Chemiresistive Gas Sensors: A Review Focused on Personalized Healthcare

Abstract: In this review, the different important parameters having significant effects on the sensing behavior of semiconductor metal oxides (SMO) based chemiresistive gas sensors have been discussed in details. Recently, SMO based chemiresistive sensors have shown immense potential in multifarious applications, especially human volatilome-based disease detection and health monitoring. In this work, we have selected some of the materials and operating condition aspects, viz. particle size and morphology, porosity, doping by noble metals and aliovalent ions, crystal phases and selectively exposed highly reactive crystalline planes, humidity, operating temperature, oxide heterojunction, homojunction and complex oxides, acid-base interaction between an oxide and a gas, gas molecule reformation inside sensing layer/ catalytic overlayer and interface gas filtration, light activation etc. and systematically reviewed their effects on the gas sensing performance of SMO sensors. From the perspective of practical applications, long-term stability, and high-throughput synthesis techniques have been elaborated. The future scope of the SMO-based breath and skin gas sensors in the upcoming area of skin mounted/wearable devices for personalized healthcare has been elucidated briefly. Finally, the discussions have been summarized with the major takeaways of this work.

Gas sensing performance of carbon monoxide at room temperature based on rod-shaped tin diselenide/MOFs derived zinc oxide polyhedron

Abstract: This paper introduces a high-efficiency CO gas sensor based on ZnO/SnSe 2 composite film. The rod-shaped SnSe 2 and polyhedral ZnO composite nanostructures were prepared by template sacrificial method and solvothermal method. The developed composite material was characterized by scanning X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and I-V testing methods, and its microstructure and composition were explored. Through comparative experiments, it was found that the response of ZnO/SnSe 2 was the highest when the loading rate of SnSe 2 is 25%, which was superior to pure ZnO and SnSe 2 sensors. The ZnO/SnSe 2 composite sensor showed excellent selectivity and good dynamic characteristics to CO at room temperature (RT). To further improve the performance of the prepared CO sensor, we studied the effect of ultraviolet (UV) light on the sensor, and the research concluded that UV light can improve the gas-sensing characteristics of the sensors. The possible CO sensing mechanism is related to the heterostructure between n-type SnSe 2 and n-type ZnO nanomaterials and the photoelectrons excited by UV light. • The rod-shaped SnSe 2 and polyhedral ZnO composite nanostructures were prepared by template sacrificial method. • The ZnO/SnSe 2 heterostructures exhibited an enhancement of CO sensing properties at room temperature. • The sensing performances of ZnO/SnSe 2 to CO were significantly improved with the irradiation of UV light.

MXene modulated SnO2 gas sensor for ultra-responsive room-temperature detection of NO2

Abstract: Continuous exposure to high concentration of nitrogen dioxide (NO 2 ) severely affects the human respiratory system. Besides, NO 2 has been recently observed to foster COVID-19, resulting in increased fatality rate; thus highly selective gas sensors are required for detecting NO 2 at sub-ppb level. In this direction, we have synthesized two-dimensional MXene-based tin oxide (SnO 2 ) heterostructures with varying MXene wt% (10–40 wt%) using a facile hydrothermal method for room-temperature NO 2 detection. The synthesized heterostructures have been structurally, optically, and electrically characterized using a suite of characterization techniques, namely, X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and Brunauer–Emmett–Teller techniques. The optimal incorporation of MXene in SnO 2 nanoparticles effectively decumulates them, increasing the specific surface area of heterostructures and thereby exposing large number of adsorption sites. 20-wt% SnO 2 /MXene heterostructures-based sensor exhibits nearly five times higher response (231%) toward 30-ppb NO 2 at room temperature with shorter response time (146 s) and recovery time (102 s) than pristine SnO 2 . Moreover, the sensor showed high selectivity, sensitivity, repeatability, reproducibility, and stable sensing response under humid conditions. The assembly of these results suggests that SnO 2 /MXene platform provides a pathway for realizing highly responsive NO 2 sensors. Herein, possible gas sensing mechanism based on the formation of SnO 2 /MXene heterostructures has been discussed. • MXene-incorporated SnO 2 heterostructures-based sensors have been fabricated using hydrothermal method. • Optimized MXene loading enhanced response and room-temperature selectivity towards NO 2 . • Fabricated sensors are capable of detecting ppb-level NO 2 with fast response and recovery time at room temperature. • SnO 2 /MXene Schottky junctions are found responsible for enhancing the gas sensing performance.

High-sensitive NO2 sensor based on p-NiCo2O4/n-WO3 heterojunctions

Abstract: In this paper, a NO2 gas sensor with outstanding sensing performance based on NiCo2O4/WO3 nanocomposite was synthesized by a hydrothermal method. A variety of testing methods such as XRD, SEM, TEM and XPS were applied to characterize the microstructure, morphology and element compositions of the sensing material. The sensing properties of NiCo2O4/WO3 composite films to NO2 gas were studied at the optimal temperature of 150 oC. The test results of gas sensor showed that, compared with the pristine WO3 sensor, the NiCo2O4/WO3 composite film sensor had higher response (116.9@20 ppm), shorter response/recovery time (13 s/16 s@20 ppm), good linearity, stable repeatability and brilliant selectivity. The enhanced gas sensitivity of NiCo2O4/WO3 nanocomposite films may be due to the synergistic effect of the unique microstructure of NiCo2O4/WO3 and the p-n heterojunction formed between the two materials.

Recent advances in SnO2 nanostructure based gas sensors

Abstract: The detection of low-concentration gases and odors in fields such as healthcare, mobility, and indoor environment control is attracting tremendous attention. The development of high-sensitivity gas sensors capable of detecting low concentrations of gases and molecules is strongly desired. This review focuses on tin oxide nanomaterials, which are substances that are being actively researched as semiconductor-type gas sensors. In particular, the development of novel tin oxide nanomaterials over the last decade and their gas sensing applications are discussed. It is revealed that dimension and morphology affect the sensing performance. Tin oxide nanomaterials having nano-meter size which is similar to size of a depletion layer, and controlled microstructure such as a nanosheet structure shows high sensing performance. The dendritic structure in which 2D nanosheets are connected by crystal growth points the direction for future sensor development. Furthermore, the high gas adsorption performance and reactivity of the metastable crystal plane will be a guide for future sensor development.

Anchoring Fe2O3 nanosheets on NiO nanoprisms to regulate the electronic properties for improved n-butanol detection

Abstract: Metal oxide heterostructures have great potential in gas sensor devices due to the attractive chemical and electronic properties at the heterogeneous interfaces. Herein, a unique heterostructure of NiO nanoprisms/Fe 2 O 3 nanosheets is rationally designed by a solution method for use in n-butanol sensors with superior performances. Mott-Schottky tests reveal that the conductivity of the NiO sensor transforms from p-type to n-type after growing Fe 2 O 3. This conversion of conductivity plays a crucial role in improving the sensor response, which overcomes the low response of p-type metal oxides. The sensor shows good linear response within the concentration range of 0.1–20 ppm n-butanol under operating temperatures (Room Temperature-320 °C). Gas sensing investigations show the sensor based on NiO/Fe 2 O 3 has a response of 4.2–10 ppm n-butanol at an optimal temperature of 200 °C, revealing a 3-time enhancement compared to pure NiO. Meanwhile the NiO/Fe 2 O 3 sensor exhibits a detection limit of 48 ppb, which is much lower than that (296 ppb) of NiO. The proposed structural design in this work provides a new idea for synthesis of high-performance sensing materials for the detection of ppb-level n-butanol. • Fe 2 O 3 nanosheets are grown on NiO nanoprisms by wet-chemical method. • Fe 2 O 3 nanosheets improve the adsorption of reactive oxygen on NiO nanoprisms. • The NiO/Fe 2 O 3 heterostructures exhibit fast response for n-butanol detection. • The NiO/Fe 2 O 3 sensor delivers good selectivity and low detection limit to n-butanol.

Hematite nanoparticle decorated MIL-100 for the highly selective and sensitive electrochemical detection of trace-level paraquat in milk and honey

Abstract: An octahedral metal-organic framework, MIL-100, was synthesized by a hydrothermal method followed by high-temperature calcination. Thereafter, hematite nanoparticles were assembled on its surface to form Fe2O3-MIL-100, which was used to develop an electrochemical sensor for the sensitive detection of paraquat (PQ). The Fe2O3-MIL-100-based electrochemical sensor showed appreciable sensing performance under optimized conditions, with a linear response in the range of 0.01–30 μM and a limit of detection of 2.6 nM. The Fe2O3-MIL-100-based electrode produced an excellent current response to PQ even after 20 d of storage. Notably, the Fe2O3-MIL-100-based electrochemical sensor exhibited high sensitivity and selectivity for PQ detection in milk and honey samples. Therefore, the fabricated sensor can be an effective tool for the rapid detection of PQ in foods.

CRISPR/Cas12a based fluorescence-enhanced lateral flow biosensor for detection of Staphylococcus aureus

Abstract: Rapid, accurate point-of-care testing (POCT) for pathogenic bacteria detection is the key for avoiding foodborne diseases caused by pathogens or their toxins. The lateral flow biosensor (LFB) based on clustered regularly interspaced short palindromic repeats (CRISPR/Cas) has displayed remarkable potential for pathogen diagnosis. In this study, we report a novel CRISPR/Cas12a-based fluorescence enhanced LFB in conjunction with functionalized quantum dots, combined with recombinase-assisted amplification (RAA), to establish low-cost, simple, and sensitive detection of Staphylococcus aureus, namely CRA-LFB (CRISPR/Cas-recombinase-assisted amplification based LFB). The CRA-LFB assay is characterized by Cas12a-mediated trans-cleavage activation induced by the target DNA to digest biotin-DNA probes, caused no complementarity to the capture probe immobilized on the test (T) line, and resulted in an undetectable T line fluorescence signal on LFB. The naked eye or fluorescence strip reader was used to determine the fluorescence intensity of the T and control lines. The limit of detection (at optimal conditions) was as low as 75 aM of genomic DNA, and 5.4 × 102 cfu/mL of S. aureus in pure cultures were detected. Moreover, this CRA-LFB assay can rapidly and accurately detect S. aureus in spiked and natural meat and vegetable samples. The CRA-LFB method yielded high specificity and no interference from other nontargeted bacteria. The results exhibited high-resolution, high-intensity fluorescent signals obtained within 70 min. This bacterial detection platform is simple, low cost, almost equipment-free, and fully qualified for food and clinical diagnosis onsite testing requirements.

Smart dual-response probe reveals an increase of GSH level and viscosity in Cisplatin-induced apoptosis and provides dual-channel imaging for tumor

Abstract: Both glutathione (GSH) and viscosity play an important role in mitochondria. They are closely related to various physiological and pathological processes and are important biomarkers in cancer analysis. Herein, we developed the first dual responsive fluorescence probe MGV that can simultaneously detect mitochondrial GSH and viscosity. MGV is smart and shows a selective ratiometric response to GSH at 535/650 nm with a significant increase of green fluorescence. MGV can also show a distinct red fluorescence enhancement at 627 nm as viscosity increases. In addition, MGV has low cytotoxicity and good mitochondrial-targeting ability. With these features, MGV was successfully applied to image mitochondrial GSH at dual fluorescence channels and track mitochondrial viscosity changes on the red fluorescence channel. With MGV, the formation of mitochondrial bleb vesicles was observed with nystatin stimulation, and during the Cisplatin-induced apoptosis, both the level of GSH and the viscosity showed an increase. Finally, based on the dual-response to GSH and viscosity, MGV was successfully used for dual-channel imaging of cancer cells/tumors. Overall, this work provided a smart probe for GSH and viscosity and new insights/methods for apoptosis and tumor imaging.

Diketopyrrolopyrrole-based sensor for over-expressed peroxynitrite in drug-induced hepatotoxicity via ratiometric fluorescence imaging

Abstract: Early diagnosis and detection of drug-induced liver injury (DILI) is great significance for the effective prevention and treatment of patients with liver injury. Studies indicate that the up-regulation of peroxynitrite (ONOO ) levels in liver is profoundly involved in acetaminophen (APAP)-induced liver injury. Herein, we constructed diketopyrrolopyrrole (DPP)-based ratiometric fluorescent probes (DPP-DH-P and DPP-DEG-P) for detecting and imaging ONOO . Comparing two probes, DPP-DEG-P exhibited higher signal-to-noise ratio (2750-fold) and lower detection limit (3.5 nM) for tracking ONOO in solution. DPP-DH-P possessing better biocompatibility had been successfully applied to monitor the fluctuation of ONOO in LPS/IFN-γ or APAP-treated hepatocytes with a high signal-to-noise ratio (20-fold) by ratiometric imaging. Moreover, the probe was used to evaluate the repair effect of glutathione on DILI. We unexpectedly discovered that DPP-DH-P and DPP-DH targeted lysosomes and mitochondria, respectively. Based on the change of ONOO induced by APAP, we observed that DPP-DH-P and the generated DPP-DH diffused from lysosome into cytoplasm, and DPP-DH did not target mitochondria due to the effect of endogenous ONOO , these indirectly reflected the dysfunction of organelles. Observably, this work will accelerate a deeper comprehending for the pathogenesis of DILI, and furnish an effective tool for the diagnosis and treatment of DILI.

Vertical silica nanochannels supported by nanocarbon composite for simultaneous detection of serotonin and melatonin in biological fluids

Abstract: Herein we report the simultaneous determination of serotonin (5-HT) and melatonin (MT) by using highly ordered and vertically-oriented mesoporous silica-nanochannel films (VMSF) on highly electrochemically reduced graphene oxide-carbon nanotubes (HErGO-CNT) composite substrate. Such VMSF/HErGO-CNT with compact 2D–2D layered structure is fabricated on indium tin oxide (ITO) electrodes via a two-step electrochemical process, namely the electrodeposition of ErGO-CNT film onto the ITO surface by cyclic voltammetry and subsequently growth of VMSF on the ErGO-CNT/ITO surface by electrochemically assisted self-assembly method, during which graphene oxide (GO) is subjected to the two-time electrochemical reduction to form HErGO. The CNT encased in the GO sheets served as electronic conducting wires, which not only can promote the electrochemical reduction of GO but also contribute to a certain degree of hydrophobicity, facilitating the controllable electrodeposition of ErGO-CNT composites on ITO under its safe use potential window. In addition, doping CNT is able to enlarge the layer gap between graphene sheets and thus improves the electroactive area and mass transfer of the nanocarbon composite substrate. Furthermore, the underlying HErGO-CNT acts as an efficient electroactive layer and the outer VMSF possesses electrostatic preconcentration and anti-fouling functions, synergistically realizing the direct electrochemical analysis of 5-HT and MT in two complex biological fluids (human whole blood and artificial cerebrospinal fluid).

Ultrafast NH3 gas sensor based on phthalocyanine-optimized non-covalent hybrid of carbon nanotubes with pyrrole†

Abstract: The development of innovative methods for optimizing carbon nanotube-based gas sensors for rapid and sensitive detection of ammonia remains challenging. Here, [email protected]/TfmpoPcCo hybrid with a uniform 3-D network were prepared by tightly combining tetra-β-trifluoromethylphenoxyphthalocyanine cobalt (TfmpoPcCo) on the surface of [email protected] through π-π interactions and used to construct NH3 sensor, while the [email protected] were obtained by in-situ polymerization of PPy onto the side wall of MCNT. TfmpoPcCo not only adsorbs on the [email protected] side wall due to its structure advantages, but also acts as a sensor accelerator. [email protected]/TfmpoPcCo sensor show higher NH3 sensing performance than the MCNT, PPy and TfmpoPcCo under same operating conditions, especially in ultrafast response/recovery time (11.7 s/91.8 s to 50 ppm NH3) with low limit-of-detection of 11 ppb at room temperature (20 °C) and excellent gas selectivity. In addition, the [email protected]/TfmpoPcCo sensor preserve superior gas response (26.2% to 50 ppm NH3) as well as outstanding stability over 60 days and humidity resistance. The excellent NH3 sensing properties are attributed to the excellent gas selectivity of TfmpoPcCo, the unique redox characteristics of PPy to ammonia (NH3), and the good electron transport ability and stability of MCNT. The synergistic optimization strategy of ternary materials is of great significance towards the exploration and construction of ideal materials for gas sensor in the future.

SERS-based dual-mode DNA aptasensors for rapid classification of SARS-CoV-2 and influenza A/H1N1 infection

Abstract: We developed a dual-mode surface-enhanced Raman scattering (SERS)-based aptasensor that can accurately diagnose and distinguish severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A/H1N1 at the same time. Herein, DNA aptamers that selectively bind to SARS-CoV-2 and influenza A/H1N1 were immobilized together on Au nanopopcorn substrate. Raman reporters (Cy3 and RRX), attached to the terminal of DNA aptamers, could generate strong SERS signals in the nanogap of the Au nanopopcorn substrate. Additionally, the internal standard Raman reporter (4-MBA) was immobilized on the Au nanopopcorn substrate along with aptamer DNAs to reduce errors caused by changes in the measurement environment. When SARS-CoV-2 or influenza A virus approaches the Au nanopopcorn substrate, the corresponding DNA aptamer selectively detaches from the substrate due to the significant binding affinity between the corresponding DNA aptamer and the virus. As a result, the related SERS intensity decreases with increasing target virus concentration. Thus, it is possible to determine whether a suspected patient is infected with SARS-CoV-2 or influenza A using this SERS-based DNA aptasensor. Furthermore, this sensor enables a quantitative evaluation of the target virus concentration with high sensitivity without being affected by cross-reactivity. Therefore, this SERS-based diagnostic platform is considered a conceptually new diagnostic tool that rapidly discriminates against these two respiratory diseases to prevent their spread. • A dual-mode SERS-based DNA aptasensor to diagnose two viruses has been developed. • DNA aptamers-immobilized on Au nanopopcorn substrate was used as a sensing template. • This sensor enables rapid differentiation between SARS-CoV-2 and influenza A infection.

Rapid and accurate detection of highly toxic NO2 gas based on catkins biomass-derived porous In2O3 microtubes at low temperature

Abstract: Development of In 2 O 3 -based gas sensors has recently attracted widespread attention, however, how to shorten the response and recovery time for sub-ppm level NO 2 detection remains challenging. In this work, biomorphic In 2 O 3 sensing material (In 2 O 3 -600) was successfully prepared through simple indium chloride solution immersion and air calcination at 600 ℃ with waste catkins template. This hierarchical structure is cross-linked by uniform spherical nanoparticles with good crystallinity. Its multi-stage pores and 1-D microtube structure are conducive to promoting the rapid diffusion and desorption of target gas, and the existence of oxygen vacancy defects can also effectively increase the conductivity, active sites and the content of surface adsorbed oxygen species. Their synergism significantly improves the rapid response and recovery speed of sensor to trace NO 2 under low energy consumption. At 92 ℃, the response value of In 2 O 3 -600 sensor towards 10 ppm NO 2 is up to 193 with rapid response and recovery times (56 and 14 s), even 1 ppm for 64 and 32 s, which is significantly shorter than most reported In 2 O 3 -based sensors. In addition, the sensor also has a wide linear detection range, low detection limit, good selectivity, and satisfactory reproducibility, moisture resistance and long-term stability. Therefore, the biomorphic porous In 2 O 3 -600 microtubes are available as candidate for detecting sub-ppm level NO 2 gas at low temperature. • Porous In 2 O 3 microtubes were simply and controllably synthesized using waste catkin as bio-template. • In 2 O 3 -600 sensor exhibits rapid response and recovery times (64 s/32 s) to 1 ppm NO 2 at 92 ℃. • The synergism of unique microtube and oxygen vacancies is highly responsible for excellent sensing performance. • The simple catkin-template method provides useful reference for synthesizing other advanced metal oxide nanomaterials.

Liposome-encapsulated aggregation-induced emission fluorogen assisted with portable smartphone for dynamically on-site imaging of residual tetracycline

Abstract: Reliable on-site monitoring of antibiotic residue is critical to establish the efficient pollution early-warning mechanism for ensuring food safety and environmental health. Herein, we reported the engineering of liposome-encapsulated aggregation-induced emission fluorogen into the portable smartphone for achieving the visual on-site detection of residual tetracycline (TC). Through nanoprecipitation, the aggregation-induced emission fluorogen (AIEgen) tetraphenylethene (TPE) was encapsulated into an amphiphilic phospholipid polymer, affording a scaffold to assemble Eu3+ for forming Eu3+-functionalized liposome-based AIEgen (Eu3+@AIEgen) with bright blue fluorescence at ~456 nm. Upon assistance of citrate, TC was capable of triggering the remarkable fluorescence color change from bright blue (~456 nm) to pink owing to the new red fluorescence emission appeared at ~611 nm, thereby emerging a significant dual-emission for ratiometric response. As expected, an ingenious citrate-assisted Eu3+@AIEgen liposome-based smartphone was proposed to precisely on-site report the residual levels of TC in real sample among the linear range of 0.0961–10.0 μM. Furthermore, this portable sensor exhibited a high sensitivity attributable to the low detection limit of 28.83 nM together with a fast response kinetics of 2.0 min for TC, agreeing well with the demands of on-site assay. This study showed the promising potential for utilizing AIEgen liposome to develop a new category of portable sensors for the point-of-care detection of antibiotic residue in complicated food and environment-related matrixes, which might open a novel way to establish efficient pollution early-warning mechanism for safeguarding public health.

Rapid field determination of SARS-CoV-2 by a colorimetric and fluorescent dual-functional lateral flow immunoassay biosensor.

Abstract: The rapid and accurate diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the early stage of virus infection can effectively prevent the spread of the virus and control the epidemic. Here, a colorimetric and fluorescent dual-functional lateral flow immunoassay (LFIA) biosensor was developed for the rapid and sensitive detection of spike 1 (S1) protein of SARS-CoV-2. A novel dual-functional immune label was fabricated by coating a single-layer shell formed by mixing 20 nm Au nanoparticles (Au NPs) and quantum dots (QDs) on SiO2 core to produce strong colorimetric and fluorescence signals and ensure good monodispersity and high stability. The colorimetric signal was used for visual detection and rapid screening of suspected SARS-CoV-2 infection on sites. The fluorescence signal was utilized for sensitive and quantitative detection of virus infection at the early stage. The detection limits of detecting S1 protein via colorimetric and fluorescence functions of the biosensor were 1 and 0.033 ng/mL, respectively. Furthermore, we evaluated the performance of the biosensor for analyzing real samples. The novel biosensor developed herein had good repeatability, specificity and accuracy, which showed great potential as a tool for rapidly detecting SARS-CoV-2.

Ni-Co-P hollow nanobricks enabled humidity sensor for respiratory analysis and human-machine interfacing

Abstract: Metal phosphide has been widely exploited in the field of energy storage and catalysis instead of chemical sensors. In this work, Ni-Co-P hollow nanobricks (HNBs) was developed via template synthesis method followed by etching and phosphating treatments. The hierarchical morphology and composition of the Ni-Co-P HNBs were respectively characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen sorption analysis and transmission electron microscopy (TEM). High sensitivity (~ 3.6 kΩ / % RH), low hysteresis (~ 3% RH) and good repeatability were achieved in a wide moisture range from 0% RH to 97.5% RH. By adjusting the ratio of Ni and Co, humidity sensing performance can be efficiently modulated. The optimal humidity sensing properties were attained at a ratio of Ni and Co of 1:5. Finally, the as-prepared sensor demonstrates great capability in respiratory analysis and noncontact human-machine interfacing. This work opens up a new paradigm for developing high-performance wearable sensing devices.

CRISPR/Cas12a-based photoelectrochemical sensing of microRNA on reduced graphene oxide-anchored Bi2WO6 coupling with catalytic hairpin assembly

Abstract: An innovative and generic CRISPR/Cas12a-driven photoelectrochemical (PEC) biosensing platform was developed for screening of microRNA-21 (miR-21) by coupling with target-triggered catalytic hairpin assembly (CHA) and reduced graphene oxide-anchored Bi 2 WO 6 (rGO-BWO) as the photoactive material. CHA isothermal amplification involved two programmable hairpin DNA modules and miR-21 as an activator. In the presence of miR-21, the products of target-triggered CHA circuit were inserted into the Cas12a-crRNA duplex to initial trans-cleavage capacity of CRISPR/Cas12a nuclease, accompanying the digestion on alkaline phosphatase (ALP)-labeled single-stranded DNA (ssDNA)-encoded magnetic bead (MB) through the activated CRISPR system. The ALPs were detached from magnetic beads and promoted the generation of ascorbic acid (AA), which increased the photocurrent of rGO-BWO-modified electrode. The value of photocurrent was positively proportional to the level of AA, which was also linearly correlated with target concentrations. Under optimum conditions, the CRISPR-based PEC sensing system displayed satisfying photocurrent responses toward miR-21 within the range from 1.0 fM to 1.0 nM with a limit of detection of 0.47 fM. In addition, the biosensor exhibited acceptable stability and excellent selectivity. Impressively, CHA-mediated CRISPR-based PEC biosensing platform provides a universal and sensitive method for clinical cancer diagnostics and biomolecular research. • An enhanced photoelectrochemical biosensor was designed for detection of microRNA. • Reduced graphene oxide-anchored Bi2WO6 used as the photoactive materials. • Bi2WO6-based carbon materials to enhance photoelectric conversion efficiency. • Catalytic hairpin assembly utilized for target recycling. • CRSIPR/Cas12 reaction system employed for in-situ amplified photocurrent.

PrGO decorated TiO2 nanoplates hybrid nanocomposite for augmented NO2 gas detection with faster gas kinetics under UV light irradiation

Abstract: Controlling the anatase TiO2 based-rectangular nanoplates (NPs) with {001} faces have gained immense interest in gas sensors applications, since the rectangular NPs of {001} planes are highly reactive for the adsorption of oxygen species that led to significant improvement in gas sensing performance. In this work, we report on the room temperature (RT) NO2 gas sensing performances of hybrid nanocomposites with the interpenetrated network using p-Phenylenediamine-reduced graphene oxide (PrGO) decorated TiO2 NPs. The fabricated TiO2 NPs/PrGO heterostructure sensor demonstrated the superior NO2 response (∼14.9% to 100 ppm of NO2) compared to TiO2/rGO and pristine TiO2 nanoplates. On the other hand, the TiO2 NPs/PrGO heterostructure device showed high sensitivity, repeatability and excellent selectivity with short response/recovery times towards NO2 gas at RT. Further, the performances of the TiO2NPs/PrGO gas sensor was accelerated by UV irradiation (λ = 365 nm), and the response was found as ~35.68% to 100 ppm of NO2 at RT, which was ~2.35-fold times higher than the dark condition. The high gas sensing performance would be attributed to the electrical sensitization of PrGO and the ample interface between TiO2 NPs and PrGO that stimulated the charge separation with faster charge transport characteristics. Our strategy and results shed new light to exploit diverse functionalized materials to the high response gas sensors at RT.

Rapid field determination of SARS-CoV-2 by a colorimetric and fluorescent dual-functional lateral flow immunoassay biosensor

Abstract: The rapid and accurate diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the early stage of virus infection can effectively prevent the spread of the virus and control the epidemic. Here, a colorimetric and fluorescent dual-functional lateral flow immunoassay (LFIA) biosensor was developed for the rapid and sensitive detection of spike 1 (S1) protein of SARS-CoV-2. A novel dual-functional immune label was fabricated by coating a single-layer shell formed by mixing 20 nm Au nanoparticles (Au NPs) and quantum dots (QDs) on SiO2 core to produce strong colorimetric and fluorescence signals and ensure good monodispersity and high stability. The colorimetric signal was used for visual detection and rapid screening of suspected SARS-CoV-2 infection on sites. The fluorescence signal was utilized for sensitive and quantitative detection of virus infection at the early stage. The detection limits of detecting S1 protein via colorimetric and fluorescence functions of the biosensor were 1 and 0.033 ng/mL, respectively. Furthermore, we evaluated the performance of the biosensor for analyzing real samples. The novel biosensor developed herein had good repeatability, specificity and accuracy, which showed great potential as a tool for rapidly detecting SARS-CoV-2.

Sensitive and selective electrochemical sensor for serotonin detection based on ferrocene-gold nanoparticles decorated multiwall carbon nanotubes

Abstract: Serotonin, or 5-hydroxytryptamine (5-HT), is a neurotransmitter that plays a crucial role in neural activities. 5-HT deficiency is clinically related to several psychiatric disorders. Therefore, sensitive 5-HT detection is critical in the diagnosis of diseases associated with neurological disorders. Here we developed a sensitive electrochemical sensor utilizing ferrocene covalently linked gold nanoparticles on multiwall carbon nanotubes (FeC-AuNPs-MWCNT), electrocatalytic nanocomposites, to enhance 5-HT detection. FeC-AuNPs-MWCNT modified screen-printed carbon electrodes (SPCEs) provide catalytic activity towards 5-HT oxidation from both FeC and AuNPs along with the high conductance from the carbon nanotube network. The FeC-AuNPs-MWCNT was synthesized by chemically reducing AuNPs on MWCNT surfaces and covalently attaching FeC to the AuNPs. Square wave voltammetry analyses confirmed that the electrocatalytic nanocomposite modified electrodes improved the electrocatalytic activity towards 5-HT oxidation, 61 times higher than the unmodified SPCE. The sensor exhibited a sensitive response to 5-HT over a wide dynamic range from 0.05 µM to 20 µM, a limit of detection of 17 nM (S/N = 3), excellent reproducibility, and high selectivity towards 5-HT against several interferers, including ascorbic acid, urea, uric acid, dopamine, and glucose. The sensor was successfully demonstrated to detect sub-µM 5-HT in urine samples with satisfactory recoveries (98.3–104.9%) and a low relative standard deviation of less than 3%. This sensitive, selective, and cost-effective electrochemical sensor shows great promise in direct 5-HT analysis for clinical applications.

Gas sensor based on cobalt-doped 3D inverse opal SnO2 for air quality monitoring

Abstract: In this research, a semiconductor metal oxide (SMO)-based gas sensor was designed for the ultrasensitive and tunably selective detection of formaldehyde and acetone. Cobalt-doped 3D inverse opal SnO2 multilayer films (3D IO Co-SnO2 MFs) used as sensing materials were prepared with the ultrasonic nebulizing deposition (UND) method combined with a self-assembly template. The 3D IO Co-SnO2 (Co/Sn = 1:24 atom%) MF-based sensor exhibited a much higher response and lower limit of detection to the volatile organic compounds (VOC) gases because of the larger specific surface area, effective gas accessibility, high catalytic activity, and increased chemisorbed oxygen species generated by the elevation of the Fermi level and the narrowing of the band gap. More importantly, the 3D IO Co-SnO2 MF-based sensor showed dual-model gas sensing characteristics for selectively detecting formaldehyde and acetone at 200 °C and 225 °C, respectively, because of the difference of the VOC catalytic conversion and surface oxidative reaction rate that was dependent on the operating temperature.

Progress towards chemical gas sensors: Nanowires and 2D semiconductors

Abstract: There is a great interest in portable gas sensing technologies to provide real-time monitoring of indoor and outdoor air quality as well as the human health diagnostics. One-dimensional metal oxide nanowires have demonstrated improved properties compared to the conventional thick film gas sensors. Furthermore, two-dimensional semiconductor nanomaterials have shown great promise for the development of high performance functional devices owing to their unique physical, chemical and electrical characteristics. Hence, they become one of the most investigated structures for the fabrication of detection systems. Herein, we present an overview of the synthesis and sensing properties of metal oxide nanowires and two-dimensional semiconductor nanostructures such as metal-organic frameworks, graphene and transition metal dichalcogenides. We discuss the current achievements and issues in the preparation of pure, doped and composite materials comprising metal oxide nanowires and two-dimensional semiconductors. Then, we discuss the advances in gas sensing performances of the aforementioned materials considering their morphology, compositions and structure. Afterward, we provide a brief summary along with the opportunities and challenges for future fabrication of high performance and small size gas sensing devices.

Plug-in optical fiber SPR biosensor for lung cancer gene detection with temperature and pH compensation

Abstract: A novel DNA hybridization optical fiber sensor with temperature and pH compensation for detecting a common lung cancer gene of epidermal growth factor receptor (EGFR) gene was demonstrated in this paper. The paper proposes the first research to achieve dual surface plasmon resonance (SPR) in an Fiber Bragg grating (FBG) and implement a three-parameter detection of DNA sequence, temperature and pH using a single fiber. Probe DNA sequences (pDNA) and PAA/CS, a pH-sensitive material, are immobilized on the sensor surface for EGFR gene exon-20 detection and temperature and pH monitoring simultaneously. The effectiveness of this functionalized method has been proved by using an atomic force microscope (AFM) and scanning electron microscope (SEM). The limit of detection (LOD) of EGFR gene was experimentally verified to 13.5 nM. The advantages of fast response, high sensitivity, label free, plug in, low LOD and three-parameter detection demonstrated by this sensor in the experiment are important for the field of DNA hybridization research and solving the problems of biosensor susceptibility to temperature and pH.

Smart dual-response probe reveals an increase of GSH level and viscosity in Cisplatin-induced apoptosis and provides dual-channel imaging for tumor

Abstract: Both glutathione (GSH) and viscosity play an important role in mitochondria. They are closely related to various physiological and pathological processes and are important biomarkers in cancer analysis. Herein, we developed the first dual responsive fluorescence probe MGV that can simultaneously detect mitochondrial GSH and viscosity. MGV is smart and shows a selective ratiometric response to GSH at 535/650 nm with a significant increase of green fluorescence. MGV can also show a distinct red fluorescence enhancement at 627 nm as viscosity increases. In addition, MGV has low cytotoxicity and good mitochondrial-targeting ability. With these features, MGV was successfully applied to image mitochondrial GSH at dual fluorescence channels and track mitochondrial viscosity changes on the red fluorescence channel. With MGV , the formation of mitochondrial bleb vesicles was observed with nystatin stimulation, and during the Cisplatin-induced apoptosis, both the level of GSH and the viscosity showed an increase. Finally, based on the dual-response to GSH and viscosity, MGV was successfully used for dual-channel imaging of cancer cells/tumors. Overall, this work provided a smart probe for GSH and viscosity and new insights/methods for apoptosis and tumor imaging. • MGV is the first developed dual-response probe for simultaneous detection of GSH and viscosity. • MGV shows low cytotoxicity and good mitochondrial targeting ability. • MGV can be applied for imaging of GSH and viscosity in living cells. • MGV can be applied for dual-channel fluorescence imaging of apoptosis and tumor cells/tissues.